After arriving in Las Vegas, the couple headed to Planet Hollywood where they checked into their 3,100-square-foot suite designed by former Top Design host Jonathon Adler. Dubbed a "mega suite," the two-bedroom domicile overlooks the Paris Hotel's Eiffel Tower and the famed Bellagio fountains.

Not to mention, features a stunning red Murano glass chandelier in the entry way as well as a full dining room, living room and jacuzzi tub.

Spears, donning a short, nude Herve Leger dress, stepped out a few hours later and revealed her highly-anticipated Neil Lane sparkler during a congratulatory welcome on the hotel's mezzanine. Planet Hollywood Chairman Robert Earl presented Trawick with an oversized birthday cake in a quick ceremony.

"She wanted it to be quick because her kids where upstairs and she wanted to put them to bed," a source told PEOPLE.

Following the celebration, the duo stopped in at Sugar Factory's Chocolate Lounge where they shared a turkey burger and a club sandwich in a room closed off to the public to give the couple privacy. A line of waiters where later seen bringing a tray of cupcakes and a large sundae of ice cream covered in sprinkles.

And what better place to end the night than Paris's Chateau Nightclub. Surrounded by friends, Spears, 30, and Trawick, 40, hung out in their own private VIP table overlooking the club's dance floor.

"Britney seemed happy, holding Jason's hand," an onlooker said. They retreated to a private area after 1 a.m., but Spears was "dancing up a storm" until nearly 4.

Fun was definitely had, as her Facebook page reflected a new note early Saturday: "Tonight was one of the most magical nights of my life. Such an amazing time with my new fiancé and our closest friends and family."